<h2>题目编号 : 280</h2>
<div style="color:#666;font-size:80%;">27 February 2010</div><br />
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<p>A laborious ant walks randomly on a 5x5 grid. The walk starts from the central square. At each step, the ant moves to an adjacent square at random, without leaving the grid; thus there are 2, 3 or 4 possible moves at each step depending on the ant's position.</p>

<p>At the start of the walk, a seed is placed on each square of the lower row. When the ant isn't carrying a seed and reaches a square of the lower row containing a seed, it will start to carry the seed. The ant will drop the seed on the first empty square of the upper row it eventually reaches.</p>

<p>What's the expected number of steps until all seeds have been dropped in the top row? <br />
Give your answer rounded to 6 decimal places.</p>
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